1. Field of the Invention
The present invention relates to new photoresists that are suitable for short wavelength imaging, including sub-200 nm, particularly sub-170 nm such as 157 nm. Resists of the invention comprise a fluorine-containing polymer, a photoactive component, typically one or more photoacid generators, and a solvent component. Preferred solvents for use on the resists of the invention can maintain the resist components in solution and include a blend of two or more fluid materials (blend members). In particularly preferred solvent blends of the invention, each blend member evaporates at substantially equal rates, whereby the resist composition maintains a substantially constant concentration of each blend member.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4.
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of about 250 nm or less, or even about 200 nm or less, such as wavelengths of about 193 nm. Use of such short exposure wavelengths can enable formation of smaller features. Accordingly, a photoresist that yields well-resolved images upon 248 nm or 193 nm exposure could enable formation of extremely small (e.g. sub-0.25 xcexcm) features that respond to constant industry demands for smaller dimension circuit patterns, e.g. to provide greater circuit density and enhanced device performance.
Quite recently, F2 excimer laser imaging, i.e. radiation having a wavelength of about 157 nm, has been considered as a route to manufacture of even smaller features. See, generally, Kunz et al., SPIE Proceedings (Advances in Resist Technology), vol. 3678, pages 13-23 (1999).
Novel photoresist compositions are provided that comprise a fluorine-containing polymer, a photoactive component particularly a photoacid generator compound, and solvent. Resists of the invention are particularly suitable for imaging at extremely short wavelengths, such as sub-170 nm, particularly about 157 nm.
In one aspect, preferred solvents for use in resists of the invention include heptanone, particularly 2-hetaptanone (methyl-n-amyl-ketone) and 3-heptanone; ethyl-n-amyl-ketone; ethylene glycol ethyl ether; propylene glycol methyl ether acetate; amyl acetate; methyl iso-amyl ketone; methyl ethyl ketone; ethylene glycol methyl ether acetate; methylamyl acetate; ethylene glycol methyl ether acetate; ethyl-n-butyl ketone; iso-butyl isobutyrate; 2-methyl-1-pentanol (hexanol); ethylene glycol propyl ether; propylene glycol t-butyl ether; methylcaproate; ethyl caproate (ethyl hexanoate); cumene (isopropylbenzene); xylenes; anisole; cyclohexanone; ethylene glycol ethyl ether acetate; 1-tridecanol; cyclohexanol; mesitylene; hexyl acetate (2-methyl-1-pentyl acetate); diethylene glycol dimethyl ether (diglyme); diisobutyl ketone; di-n-propyl carbonate; diacetonealcohol; ethylene glycol butyl ether; and propylene glycol butyl ether.
In another aspect, preferred solvents for use in resists of the invention are halogenated materials, particularly fluorinated materials. Such halogenated solvents can be particularly effective in solubilizing a fluorinated resin of a resist of the invention. Exemplary halogenated solvents for use in resists of the invention include halogenated aromatic solvents such as chlorobenzene, fluorobenzene, trifluoromethylbenzeone, bis-(trifluoromethyl)benzene, and the like; perfluoroalkyl solvents; and fluoroethers such as HFE-700, FC-43, and FC-3248 (all available from the 3M Corporation) and other fluoroether solvents and other fluorinated solvents available from 3M Corporation; and the like.
Resists formulations are also preferred that comprise a blend of solvents, wherein one of the blend members is a heptanone, preferably 2-heptanone. Other blend members may suitably be e.g. ethyl lactate, propylene glycol methyl ether acetate (PGMEA), diacetone alcohol, hexyl acetate, ethyl hexanoate, gamma-butyrolactone (GBL), diglyme, propylene glycol dimethyl ether, and propylene glycol methyl ether.
Other solvent blends for use with resists of the invention include blends that comprise other ketones or other carbonyl functionalities (e.g., ester). It has been found that solvents that contain a carbonyl group can solvate a fluoropolymer more effectively than other non-carbonyl solvents. In particular, cyclohexanone, various dialkyl-ketone such as diisobutyl ketone and ethoxy ethyl propionate are preferred solvents for are use in a resist formulation of the invention, including as a blend member with one or more other solvents such as ethyl lactate, propylene glycol methyl ether acetate (PGMEA), diacetone alcohol, hexyl acetate, ethyl hexanoate, gamma-butyrolactone (GBL), diglyme, propylene glycol dimethyl ether, and propylene glycol methyl ether. In general, a ketone solvent such as a heptanone or dissobutyl ketone, is more preferred than an ester-containing solvent such as ethyl ethoxy propionate.
Solvent blends of resist formulations of the invention may suitably comprise two or three or more different solvents in a single blend, more typically two or three distinct solvents. Preferably a carbonyl solvent, such as a heptanone, diissobutyl ketone, is present in a solvating effective amount, i.e. an amount wherein the carbonyl solvent itself is effective in dissolving the resist components.
A preferred component of a resist solvent blend of the invention is a halogenated solvent such as those discussed above. Enhanced solubilization can be realized in many cases with the halogenated solvent present as even a minor component of the solvent blend, e.g. where one or more halogenated solvents comprise about 50 volume percent or less of the total solvent of a resist composition, or where one or more halogenated solvents comprise about 40, 30, 25, 20, 15, 10, 5, 3 or even 2 volume percent or less of the total solvent of a resist composition. A solvent blend of a resist composition of the invention also may contain greater amounts of one or more halogenated solvents, e.g. where one or more halogenated solvents comprise about 55, 60, 70, 80, 90 or 95 volume percent or more of the total solvent of a resist composition. One or more halogenated solvents are preferably used in a solvent blend that comprises other solvents that contain carbonyl and/or hydroxy moieties, e.g. a heptanone, cyclohexanone, ethyl lactate, and the like.
Another preferred component of a resist solvent blend of the invention is water. It is believed water may stabilize a solvent blend and a resist composition, e.g. render a photoacid generator compound more resistant to degradation during storage. Water present as residual solvent after a soft-bake step also may facilitate a deprotection reaction of photoacid-labile groups present in a resist composition. Preferably, water will be present in relatively small amounts in a resist composition, e.g. where water constitutes no more than about 10, 8, 6, 5, 4, 3, 2, 1, 0.5 or 0.25 volume percent of the total solvent of a resist composition. Generally preferred is where water is present in no more than about 3, 2, 1, 0.5 or 0.25 volume percent of the total solvent component of a resist composition. Water preferably will be employed in a solvent blend that comprises other solvents that contain carbonyl and/or hydroxy moieties, e.g. a heptanone, cyclohexanone, ethyl lactate, and the like.
Particularly preferred solvent blends of the invention will vaporize from a resist formulation at substantially constant rates, whereby blend members remain at substantially equal concentrations in the resist composition. In particular, preferred are solvent blends which can form azeotropes at about room temperature, thereby evaporating from a resist liquid formulation at a constant rate, maintaining a substantially constant ratio of solvent blend members in the resist composition. By maintaining a substantially constant ratio of blend members throughout coating and soft-bake treatment, lithographic properties of the resist can be improved as may be related to enhanced film-forming characteristics of the resist, e.g. avoidance of undesired crystallization or other precipitation of resist components, irregular film layer formation, undesired segregation of polymer chains, and the like.
In addition to a fluorine-polymer and photoactive component, resists of the invention may suitably comprise one or more other components, such as a basic additive, a dissolution inhibitor compound which preferably is a polymeric and/or fluorinated composition, surfactant or leveling agent; and a plasticizer. Preferred resists of the invention also may comprise a blend of two or more resin components, preferably where each blend member is a fluorine-containing resin, and/or a blend of two or more photoacid generator compounds.
The invention also includes methods for forming relief images, including methods for forming a highly resolved relief image such as a pattern of lines (dense or isolated) where each line has vertical or essentially vertical sidewalls and a line width of about 0.40 microns or less, or even about 0.25, 0.20, 0.15, or 0.10 microns or less. In such methods, preferably a coating layer of a resist of the invention is imaged with short-wavelength radiation, particularly sub-200 nm radiation, especially 157 nm radiation, and higher energy radiation having a wavelength of less than 100 nm, and otherwise high energy radiation such as EUV, electron beam, ion beam or x-ray. The invention further comprises articles of manufacture comprising substrates such as a microelectronic wafer having coated thereon the photoresists and relief images of the invention. Other aspects of the invention are disclosed infra.